urstiinTy ri-corhers 249 



.iIhuii 'J.') ItH-i \ 27 It'i't .mil li.ivinj; two windows i-,nli in llic cist ami 

 south walls. Tlu' wind tiunu-l i't|iii|)infnt was installed at a luinlit ui 

 six fivt iijH)H a pillar in the center of the room. About ten |x,'ople 

 nornuillv work in this hmmii. The outdoor conditions were ohtaincc? 

 !)> mountinj; a winil tunnel wiuiiinient in a standard Weather Bureau 

 instrument shelter placed at the top of a tower, 14 feet lii^h, which 

 stands f)n the roof t)f a three story l)uildinj( far enouj^h away from 

 walls and other obstacles to jwrniit free circulation of the air. 



Fi>;s. 7 and 8 show two typical 12 hour records upon which the 

 ind(M)r and outdoor relative humiililies have been plotted from the 

 curves of temiK>ratures and temperature differences recorded by the 

 instrinnent. A stutl\- of these recorils indicates that large ilifTerences 

 often exist between the indoor and outdoor conditions and that the 

 indoor conditions are nuich less severe than might be expected when 

 the outdoor humidity is high. This difference is particularly notice- 

 able when the windows are closed, but as soon as they are opened the 

 indoor temperature decreases and the humidity generally increases 

 to practically the siime value as that of the outside air. Pig. 8 is 

 of particular interest in showing the rapid decrease in the outdoor 

 temperature and increase in relative liuniidit\- due to a thunder- 

 storm. 



The analysis of the records obtained from a number of recorders 

 which record temperature anti difference between dry and wet bulb 

 temperature recjuires c(»nsiderablc labor in obtaining the correspond- 

 ing relative humidities from the psychrometric tables and, obviously, 

 periodic values only can be taken unless some rapid mechanical 

 method of doing this is employed. Such methods have been developed 

 and uschI successfully for this purpose. 



.-\ Ni-.w DiRix r Ri;.\i)iNc; Himiditv Riccordiir 



A nuich more satisfactory type of recorder is one which, in additif)n 

 to tracing the temperature curve, traces a curve of the relative 

 humidity. The only instrument of any prominence that has been 

 used in this way is the recording hair hygrometer, the objectionable 

 features of which have already been mentioned. 



An improved t\pe of direct reading humidit\' recorder which has 

 lieen developed by E. B. Wood, of the Laboratories of the American 

 Telephone and Telegraph Company- and the Western Electric Com- 

 pany, employs the Leeds & Northrup automatic recorder mechanism, 

 to which has been added an electrical mechanism which will be de- 

 scribefl, together with the principle upon which its operation is based. 



